Microphones Part 2 - Directional Patterns

This week I would like to take a look at the different directional patterns of microphones and how to select the proper one for the audio you want to capture. With any of the microphone types that we mentioned in the last post, different directional patterns of response can be produced.

Directional patterns or directionality is the microphone's sensitivity to sound from variou directions. Some microphones pick up sound equally from all directions, others pick up sound only from one direction or a particular combination of directions. The types of directionality are divided into three main categories:


OMNI-DIRECTIONAL
Picks up sound evenly from all directions.

Uses:
Capturing ambient noise; Situations where sound is coming from many directions; Situations where
the mic position must remain fixed while the sound source is moving.

Notes:
Although omnidirectional mics are very useful in the right situation, picking up sound from every direction
is not usually what you need. Omni sound is very general and unfocused - if you are trying to capture sound
from a particular subject or area it is likely to be overwhelmed by other noise.


UNI-DIRECTIONAL
Microphones in this category pick up sound more strongly from one direction. While there are a number of mics under this category, I am going to look at a few of the most popular Uni-Directional Mics.


Cardoid
Picks up sound predominantly from one direction. Cardioid means "heart-shaped", which is the type of pick-up pattern these mics use. Sound is picked up mostly from the front, but to a lesser extent the sides as well.

Cardoid Uses:
Emphasising sound from the direction the mic is pointed whilst leaving some latitude for mic movement
and ambient noise.

Cardoid Notes:
The cardioid is a very versatile microphone, ideal for general use. Handheld mics are usually cardioid.


Hypercardoid
This is exaggerated version of the cardioid pattern. It is very directional and eliminates most sound from the sides and rear. Due to the long thin design of hypercardioids, they are often referred to as shotgun microphones.

Hypercardoid Uses:
Isolating the sound from a subject or direction when there is a lot of ambient noise; Picking up sound from a subject at a distance.

Hypercardoid Notes:
By removing all the ambient noise, unidirectional sound can sometimes be a little unnatural. It may help to add a discreet audio bed from another mic (i.e. constant background noise at a low level).
You need to be careful to keep the sound consistent. If the mic doesn't stay pointed at the subject you will lose the audio. Shotguns can have an area of increased sensitivity directly to the rear.


BI-DIRECTIONAL
Uses a figure-of-eight pattern and picks up sound equally from two opposite directions.

Uses:
As you can imagine, there aren't a lot of situations which require this polar pattern. One possibility would be an interview with two people facing each other (with the mic between them).


VARIABLE DIRECTIONALITY - Is "Three in one" better?
Some microphones allow you to vary the directional characteristics by selecting omni, cardioid or shotgun patterns. This feature is sometimes found on video camera microphones, with the idea that you can adjust the directionality to suit the angle of zoom, e.g. have a shotgun mic for long zooms. Some models can even automatically follow the lens zoom angle so the directionality changes from cardioid to shotgun as you zoom in. Although this seems like a good idea (and can sometimes be handy), variable zoom microphones don't perform particularly well and they often make a noise while zooming. Using different mics will usually produce better results.